Fiber based thermoelectric device

ABSTRACT

Methods of making various fibers are provided including co-axial fibers with oppositely doped cladding and core are provide; hollow core doped silicon carbide fibers are provided; and doubly clad PIN junction fibers are provided. Additionally methods are provided for forming direct PN junctions between oppositely doped fibers are provided. Various thermoelectric generators that incorporate the aforementioned fibers are provided.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with government support under ONR contract#N68335-17-C-0060 awarded by the United States Department of the Navy.The government has certain rights in the invention.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application is based on provisional patent application Ser.No. 62/887,122 filed Aug. 15, 2019.

FIELD OF THE INVENTION

The present invention relates generally to thermoelectric devices.

BACKGROUND

Thermoelectric materials may be used in systems that harness electricalpower for cooling and for systems that generate electrical power inresponse to a temperature difference between a heat source and a heatsink.

Cooling in response to an electrical current passed through athermoelectric device is a manifestation of the Peltier effect. A basicdevice that manifests the Peltier effect and hence may be used forcooling includes two dissimilar materials having a junction thermallycoupled to a thermal load to be cooled. The Peltier effect is describedby equation 1 below:{dot over (Q)}=(Π_(A)−Π_(B))·I  EQU. 1

-   -   where {dot over (Q)} is a net quantify of heat flow to the        junction;    -   Π_(A) and Π_(B) are respectively the Peltier coefficient of the        aforementioned two dissimilar materials; and    -   I is a current passed through the junction.    -   Selection between heating and cooling of the junction can be        achieved by changing the direction of the current I through the        junction;

The generation of electricity in response to the establishment of athermal gradient across a thermoelectric device is a manifestation ofthe Seebeck effect. The construction of a basic device that manifeststhe Seebeck effect parallels the construction of a basic device thatmanifests the Peltier effect. The two devices do differ however in themanner of use. In the case of the Seebeck effect electrical output isobtained in response to subjecting the device to a thermal gradientwhereas in the case of the Peltier effect heat is transferred inresponse to application of electrical power from a separate externalpower source. The Seebeck effect for a single conductor is described byequation 2 below.J=σ·(−∇V+E _(Peltier))  EQU. 2

where,

-   -   J is a current generated due to the Seebeck effect;    -   σ is an electrical conductivity of the device;    -   ∇V is an externally measured voltage; and        E _(Peltier) =S·ΔT    -   Where,    -   S is the Seebeck coefficient; and    -   ΔT is the temperature gradient across the device.

By forming a junction between a P-doped semiconductor and N-dopedsemiconductor, both of which manifest the Seebeck effect and exposingthe junction to a heat source, a continuous current can be induced toflow between proximal ends of the two semiconductors which are situatedat a position removed from the heat source.

FIG. 1 shows a prior art thermoelectric generator 100. Thethermoelectric generator 100 includes n-doped block 102 and a p-dopedblock 104. A first end 102 a of the n-doped block 102, and a first end104 a of the p-doped block 104 are contact a common hot side electricalcontact 106 which also serves as a heat source contact for coupling to aheat source (not shown) such as an exhaust manifold of an internalcombustion engine. A second end 102 b of the n-doped block 102 iscoupled to first cold side electrical contact (cathode) 108 and a secondend 104 b of the p-doped block is coupled to a second cold sideelectrical contact (anode) 110. The cold side electrical contactelectrical contacts 108, 110 are supported on a heat sink thermalcontact 112 which in use may be connected to a heat sink (not shown).Common thermoelectric materials are brittle material and hence cannot bebent near the hot side to form a direct junction between the n-dopedblock 102 and the p-doped block 104. Aside from the low complianceissue, methods of forming a PN junction from blocks of p-doped andn-doped materials may not be available. Hence the hot side electricalcontact 106 is provided to connect the n-doped block 102 and the p-dopedblock 104. Now generally speaking the efficiency of the thermoelectriceffect and the amount of electrical power that can be extracted from athermoelectric device depends on the magnitude of the temperaturedifference between the heat source (hot side) temperature and the heatsink (cold side) temperature. The cold side temperature is tied to theambient temperature and differs therefrom by an amount proportional tothe thermal resistance of the heat sink, so the best that can be done inrespect to the cold side temperature is to approach the ambienttemperature. A limiting factor in the temperature difference that may beachieved is then dependent on the maximum temperature that the hot sideof the thermoelectric generator can withstand. In the prior artthermoelectric generator 100 the limiting factor may be the temperaturelimit of the common hot side electric contact 106 which may be made ofmetal. In certain applications it would be desirable to eliminate thecommon hot side electrical contact, so as to allow a higher hot sidetemperature and greater electrical output. The maximum servicetemperature of the P and or N thermoelectric materials may also limitthe hot-cold side temperature difference that may be achieved. It wouldbe desirable to provide a thermoelectric generator that includesthermoelectric materials that are able to sustain high temperatureoperation and are also unfettered by the temperature limits typicallyassociated with hot side interconnect metallization.

SUMMARY OF THE INVENTION

One aspect of the invention is a thermoelectric generator including aheat source contact, a heat sink contact, and a plurality of co-axialfibers, each of the co-axial fibers including a core and a claddingdisposed about the core, the plurality of co-axial fibers extending fromthe heat source contact to the heat sink contact. In such athermoelectric generator the heat sink contact may include a firstelectrical contact and a second electrical contact, and the core of theco-axial fibers may extend beyond the cladding so as to present anexposed portion of the core, the cladding may be electrically coupled tothe first electrical contact and the core may be electrically coupled tothe second electrical contact. The heat source contact may include ahole and the plurality of co-axial fibers may have ends inserted in thehole. The plurality of co-axial fibers may have a serpentine shape thatmeanders back and forth between the heat source contact and the heatsink contact. In relation to the latter option the heat sink contact mayfurther include a first electrical contact and a second electricalcontact and in proceeding along a length of a particular co-axial fiberof the plurality co-axial fibers, the particular coaxial fiber includes:a first portion at which the cladding is electrically coupled to thefirst electrical contact; a second portion thermally coupled to the heatsource contact; a third portion at which the core is exposed and iselectrically coupled to the second electrical contact.

Another aspect of the invention includes a spinneret for spinning aco-axial fiber with an interrupted cladding. Such a spinneret includes:an inner conduit configured to conduct a flow of a first material forforming a core of the co-axial fiber, the inner conduit having an innerconduit inlet for receiving the first material and an inner conduitoutlet for discharging the first material; an outer chamber configuredto conduct a flow of a second material for forming a cladding of theco-axial fiber, the outer chamber having an outer chamber inlet forreceiving the second material and an outer chamber outlet fordischarging the second material, wherein the inner conduit passesthrough the outer chamber and the inner conduit outlet is disposed inthe outer chamber outlet; and a valve mechanism configured forselectively stopping the flow of the second material. The valvemechanism may include a plunger disposed in the outer chamber around theinner conduit and a biasing element for urging the plunger into theouter chamber outlet to interrupt the flow of the second material. Asolenoid may be disposed proximate the plunger and configured tocounteract the biasing element and withdraw the plunger from the outerchamber outlet so as to allow the flow of the second material.

Another aspect of the invention is a thermoelectric fabric having afirst set of conductive threads extending in a first direction, a secondset of conductive threads extending in the first direction, and a set ofco-axial thermoelectric fibers generally extending in a second directionand woven through the first set of conductive threads and the second setof conductive threads, each of the set of co-axial thermoelectric fibersincluding a core having a first type doping and a cladding having asecond type doping, wherein the cladding contacts the first set ofconductive threads, and wherein the core contacts the second set ofconductive threads. A portion of the thermoelectric fibers may be loopedsuch that the thermoelectric fabric is a looped fabric.

Another aspect of the invention includes a thermoelectric generatorincluding: a heat source contact, a plurality of N doped hollow fibershaving first ends thermally coupled to the heat source contact, aplurality of P doped hollow fibers having first ends thermally coupledto the heat source contact, a first electrical contact electricallycoupled to second ends of the plurality of N doped hollow fibers, and asecond electrical contact electrically coupled to the second ends of theplurality of P doped hollow fibers.

Another aspect of the invention includes a thermoelectric fiberincluding: an outer cladding including semiconductor having a first typeof doping; an inner core including seeming conductor having a secondtype of doping; and an inner cladding disposed between the inner coreand the outer cladding.

Another aspect of the invention includes a spinneret for forming adoubly clad core co-axial fiber, the spinneret including: an innerconduit configured to conduct a flow of a first material for forming acore of the co-axial fiber, the inner conduit having an inner conduitinlet for receiving the first material and an inner conduit outlet fordischarging the first material; an intermediate chamber configured toconduct a flow of a second material for forming an inner cladding of theco-axial fiber, the intermediate chamber having an intermediate chamberinlet for receiving the second material and an intermediate chamberoutlet for discharging the second material, wherein the inner conduitpasses through the intermediate chamber; and the inner conduit outlet isdisposed in the intermediate chamber outlet; and an outer chamberconfigured to conduct a flow of a third material for forming an outercladding of the co-axial fiber, the outer chamber having an outerchamber inlet for receiving the third material and an outer chamberoutlet for discharging the third material, wherein the intermediatechamber outlet is disposed in the outer chamber outlet.

Another aspect of the invention includes a thermoelectric deviceincluding: a P doped thermoelectric fiber having a first end and an Ndoped thermoelectric fiber having a first end wherein the first end ofthe P doped thermoelectric fiber is directly contacting the first end ofthe N doped thermoelectric fiber forming a PN junction. Thethermoelectric device may include a heat source coupler thermallycoupled to the PN junction. The N doped thermoelectric fiber has asecond end and the P doped thermoelectric fiber has a second end. Thethermoelectric device further includes a first electrical contact and asecond electrical contact, the second end of the N doped thermoelectricfiber is electrically coupled to the first electrical contact and thesecond end of the P doped thermoelectric fiber is electrically coupledto the second electrical contact. A heat sink may be thermally coupledto the first electrical contact and the second electrical contact.

Another aspect of the invention is a method of making a thermoelectricdevice. The method includes: preparing a first batch of silicon carbideprecursor mixed with a first type of dopant species; preparing a secondbatch of silicon carbide precursor mixed with a second type of dopantspecies; supplying the first batch of silicon carbide precursor mixedwith the first type of dopant species to a first inlet of a co-axialspinneret; suppling the second batch of silicon carbide precursor mixedwith the second type of dopant species to a second inlet of a co-axialspinneret; using the co-axial spinneret to spin a co-axial clad coresilicon carbide precursor fiber; pyrolizing the co-axial clad coresilicon carbide precursor fiber to obtain a co-axial clad core siliconcarbide fiber; and assembling the co-axial clad core silicon carbidefiber precursor into the thermoelectric device.

Another aspect of the invention is a method of making a hollowthermoelectric fiber. The method includes; preparing a fugitive corespinning feed stock; preparing a cladding spinning feed stock includingsilicon carbide precursor and dopant; supplying the cladding feed stockto an outer annular conduit of a spinneret; supplying the fugitive corespinning feed stock to an inner conduit of the spinneret; using thespinneret to spin a fiber having a cladding including the claddingspinning feed stock and a core including the fugitive core spinning feedstock; and heating the fiber to transform the cladding feed stock todoped silicon carbide and to eliminate the core.

Another aspect of the invention is a method of making a PN junction. Themethod includes: obtaining a first batch of silicon carbide precursorincluding a first type of dopant; obtaining a second batch of siliconcarbide precursor including a second type of dopant; spinning a firstprecursor fiber from the first batch of silicon carbide precursorincluding the first type of dopant; pyrolizing the first precursor fiberto obtain a first silicon carbide fiber having the first type of dopant;spinning a second precursor fiber from the second batch of siliconcarbide precursor including the second type of dopant; contacting thesecond precursor fiber with the first silicon carbide fiber; heating thesecond precursor fiber that is in contact with the first silicon carbidefiber to a temperature sufficient and pyrolize the second precursorfiber to obtain second silicon carbide fiber having the second type ofdopant in contact with the first silicon carbide fiber having the firsttype of dopant forming the PN junction.

Another aspect of the invention is another method of making a PNjunction that includes: obtaining a first batch of silicon carbideprecursor including an N type dopant; spinning a first precursor fiberfrom the first batch of silicon carbide precursor; obtaining a secondbatch of silicon carbide precursor including a P type dopant; spinning asecond precursor fiber from the second batch of silicon carbideprecursor; contacting the first precursor fiber and the second precursorfiber; subjecting the contacted first and second precursor fibers toheat and pyrolize the first and second precursor fibers to obtain an Ndoped silicon carbide fiber in contact with a P doped silicon carbidefiber thereby forming a PN junction.

Another aspect of the in invention is a jet engine including an outerhousing, a combustion chamber and a thermoelectric generator thermallycoupled to the outer housing and to the combustion chamber. Thethermoelectric generator may include semiconductor fibers.

Another aspect of the invention is a rocket engine including a doublewalled nozzle including an inner wall, an outer wall and athermoelectric generator located between the inner wall and the outerwall and thermally coupled to the inner wall and to the outer wall.

Another aspect of the invention is a method of forming a semiconductorjunction including: obtaining silicon carbide semiconductor having afirst doping type obtaining a silicon carbide precursor that includes asecond doping type species, contacting the silicon carbide precursorwith the silicon carbide semiconductor and pyrolyzing the siliconcarbide precursor.

Another aspect of the invention is a method of forming a semiconductorjunction comprising, the method including: obtaining a first siliconcarbide precursor having a first doping type species, obtaining a secondsilicon carbide precursor having a second doping type species,contacting the first silicon carbide precursor and the second siliconcarbide precursor, and pyrolyzing the first silicon carbide precursorand the second silicon carbide precursor.

BRIEF DESCRIPTION OF THE FIGURES

The accompanying figures, where like reference numerals refer toidentical or functionally similar elements throughout the separate viewsand which together with the detailed description below are incorporatedin and form part of the specification, serve to further illustratevarious embodiments and to explain various principles and advantages allin accordance with the present invention.

FIG. 1 shows a prior thermoelectric generator;

FIG. 2 shows a co-axial clad core thermoelectric fiber according to anembodiment of the invention;

FIG. 3 a shows a thermoelectric generator employing multiple co-axialclad core thermoelectric fibers of the type shown in FIG. 2 ;

FIG. 3 b shows a partially exploded view of the thermoelectric generatorshown in FIG. 3 a;

FIG. 4 a is a first perspective view of a thermoelectric generator thatincludes co-axial clad core fibers having a meandering contour thatalternately touches a heat source contact and a heat sink contactaccording to another embodiment of the invention;

FIG. 4 b is a second perspective view of the thermoelectric generatorshown in FIG. 4 a;

FIG. 5 a is a front view of a spinneret used to spin co-axial clad corefibers along with a schematically illustrated high voltage source and acollector according to an embodiment of the invention;

FIG. 5 b is a cross-sectional view of the spinneret shown in FIG. 5 a;

FIG. 6 a shows a broken out sectional front view of a spinneret forspinning co-axial clad core fiber including an electromagnetic valve forselectively interrupting a flow of cladding spinning solution and shownwith the valve in a closed state according to an embodiment of theinvention;

FIG. 6 b is a broken out sectional view of the spinneret shown in FIG. 6a with the electromagnetic valve in an open state;

FIG. 7 shows a perspective view of a thermoelectric cloth according toan embodiment of the invention;

FIG. 8 a is a perspective end view of a hollow thermoelectric fiberaccording to an embodiment of the invention;

FIG. 8 b is a side view of the hollow thermoelectric fiber shown in FIG.8 a;

FIG. 8 c is a cross-sectional side view of the thermoelectric fibershown in FIGS. 8 a , 8 b;

FIG. 9 a is perspective view of a thermoelectric generator includinghollow thermoelectric fibers of the type shown in FIGS. 8 a -8 c;

FIG. 9 b is a partially exploded view of the thermoelectric generatorshown in FIG. 9 a;

FIG. 10 is a side view of a doubly clad P-I-N co-axial fiber accordingto an embodiment of the invention;

FIG. 11 is a broken out sectional elevation view of a spinneret forspinning the doubly clad co-axial fiber shown in FIG. 11 ;

FIG. 12 a is a first perspective view of a thermoelectric generator thatincludes a direct PN junction between thermoelectric fibers according toan embodiment of the invention;

FIG. 12 b is a partially exploded perspective view of the thermoelectricgenerator shown in FIG. 12 a;

FIG. 13 is a flowchart of a method of making a PN co-axial clad corethermoelectric fiber according to an embodiment of the invention;

FIG. 14 is a flowchart of a method of making a hollow thermoelectricfiber according to an embodiment of the invention;

FIG. 15 is a flowchart of a first method of forming a device including aP doped fiber and an N doped fiber joined to form a PN junctionaccording to an embodiment of the invention;

FIG. 16 is a flowchart of a second method of forming a device includinga P doped fiber and an N doped fiber joined to form a PN junctionaccording to an embodiment of the invention;

FIG. 17 is a first perspective view of a thermoelectric generator modulethat includes direct PN junctions between semiconductor fibers on a heatsource contact side;

FIG. 18 is a second perspective view of the thermoelectric generatormodule shown in FIG. 18 showing PN junctions between semiconductorfibers inserted into black body cavity holes in the heat source contact;

FIG. 19 is a first perspective view of a thermoelectric generator thatincludes multiple modules of the type shown in FIGS. 17-18 ; and

FIG. 20 is a second perspective view of a thermoelectric generator shownin FIG. 19 ;

FIG. 21 is a first perspective view of a thermoelectric generator modulethat includes direct PN junctions between semiconductor fibers at both aheat source contact and a heat sink contact; and

FIG. 22 is a second perspective view of the thermoelectric generatormodule shown in FIG. 21 ;

FIG. 23 is a cross-sectional view of a jet engine that includes asemiconductor fiber based thermoelectric generator according to anembodiment of the invention;

FIG. 24 is an enlarged broken out portion of the jet engine shown inFIG. 23 including the semiconductor fiber based thermoelectric generatorposition around a combustion chamber of the jet engine;

FIG. 25 shows a partially sectioned portion of a rocket engine includinga double walled nozzle accommodating a semiconductor fiber basedthermoelectric generator according to an embodiment of the invention;

FIG. 26 is a graph including plots, for three test runs, of voltageversus temperature difference between hot and cold sides for athermoelectric generator according to an embodiment of the invention;

FIG. 27 is a graph including plots, for three test runs, of Seebeckcoefficient versus temperature difference between hot and cold sides forthe same thermoelectric generator for which data is shown in FIG. 26 ;

FIG. 28 is a graph including plots, for three test runs, of Seebeckcoefficient versus temperature difference between hot and cold sides foranother thermoelectric generator according to an embodiment of theinvention;

FIG. 29 is a scanning electron micrograph of a hollow porous SiCsemiconductor fibers that may be used in a thermoelectric generatoraccording to certain embodiments of the invention

FIG. 30 is a graph including plots, for four test runs, of Seebeckcoefficient versus average temperature of hot and cold sides for athermoelectric generator including the hollow and porous SiC fibersshown in FIG. 29 .

Skilled artisans will appreciate that elements in the figures areillustrated for simplicity and clarity and have not necessarily beendrawn to scale. For example, the dimensions of some of the elements inthe figures may be exaggerated relative to other elements to help toimprove understanding of embodiments of the present invention.

DETAILED DESCRIPTION

Before describing in detail embodiments that are in accordance with thepresent invention, it should be observed that the embodiments resideprimarily in combinations of method steps and apparatus componentsrelated to thermoelectric devices. Accordingly, the apparatus componentsand method steps have been represented where appropriate by conventionalsymbols in the drawings, showing only those specific details that arepertinent to understanding the embodiments of the present invention soas not to obscure the disclosure with details that will be readilyapparent to those of ordinary skill in the art having the benefit of thedescription herein.

FIG. 2 shows a co-axial clad core thermoelectric fiber 200 according toan embodiment of the invention. The thermoelectric fiber 200 includes acore 202 and a cladding 204 concentric with and surrounding the core202. The core 202 and the cladding 204 are electrically conductivematerials. The core 202 and the cladding 204 may have opposite typecharge carriers. The core 202 may be an n-doped semiconductor materialthat predominantly has electron charge carriers whereas the cladding 204may be a p-doped semiconductor material that predominantly has holecharge carriers. Alternatively, the core 202 may be p-doped and thecladding 204 may be n-doped. There is an exposed end portion 206 of thecore 202 that is not covered by the cladding 204 in order to facilitateelectric connection to the core 202.

Materials that may be used for the core 202 and/or the cladding 204include semiconductors such as: silicon carbide, boron carbide, silicon,silicon-germanium; metals such as bismuth telluride, bismuth antimonytelluride; and/or polymers such as polyaniline polysulfane, PEDOT:PSS,poly(3,4-ethylenedioxythiophene) polystyrene sulfate, semiconductorpolymers Pqt12, p3ht, doped polyphenylene sulphone, poly(3,3′″-dialkylquaterthiophene) (PQT-12), or Poly(3-hexylthiophene(P3HT).

The thermoelectric fiber 200 may be made by co-axial spinning, co-axialelectrospinning or co-axial extrusion. Whereas spinning typicallyinvolves using a solvent, extrusion is typically performed at atemperature above room temperature and does not include the use of asolvent.

Due to the Seebeck effect when two ends of the thermoelectric fiber areheld at two different temperatures an electromotive force will begenerated at the junction between the core and the cladding and anassociated electric current may be extracted by connecting leads of anelectrical load (not shown) to the core and the cladding in the vicinityof the end which is held at the lower temperature.

FIG. 3 a shows a thermoelectric generator 300 employing multipleco-axial clad core thermoelectric fibers 200 of the type shown in FIG. 2; and FIG. 3 b shows a partially exploded view of the thermoelectricgenerator 300 shown in FIG. 3 a . The thermoelectric generator 300includes a heat source contact 302 that includes an oblong blind recess304 into which first ends 200 a of several of the thermoelectric fibers200 are inserted. The cross-sectional shape of the recess 304 may beother than oblong, for example circular. Rather that providing a singlerecess 304, multiple recesses may be provided. The aforementionedexposed end portions of the core 206 are located proximate a second ends200 b of the thermoelectric fibers 200 and are in contact with a firstelectrical contact 306 of a heat sink contract 308. Contact portions ofthe cladding 200 c that are located proximate the exposed end portionsof the core 206, between the exposed portions of the core 206 and thefirst ends 200 a of the thermoelectric fibers 200 are in contact with asecond electrical contact 310 of the heat sink contact 308. The heatsink contact 308 is in contact with a heat sink 312. The heat sinkcontact 308 may be electrically insulating and thermally conducting. Theheat source contact 302 may be thermally coupled to a heat source (notshown) such as an exhaust manifold of an internal combustion engine oranother high temperature heat source. The heat source contact 302 mayalso be placed proximate the focus of a solar concentrator. The heatsink contact 308 may be made of a refractory material so as to withstandbeing in contact with a high temperature heat source. Note that nometallization is required to thermally couple the thermoelectric fibers200 to the heat source contact 302. At high temperatures thermalcoupling between the heat source contact 302 and the thermoelectricfibers 200 may be dominated by radiative heat transport. Providing therecess 304 into which the thermoelectric fibers 200 are inserted fostersthe aforementioned radiative heat transfer. In operation when atemperature difference is established between the heat source contact302 and the heat sink contact 308 a thermoelectrically induced voltagewill be established between core 202 and the cladding 204 of thethermoelectric fibers and consequently between the first electricalcontact 306 and the second electrical contact 310. By connecting anexternal load (not shown) to the electrical contacts 306 310 power canbe extracted from the thermoelectric generator 300.

FIG. 4 a is a first perspective view of a thermoelectric generator 400that includes co-axial clad core fibers 402 having a meandering contourthat alternately touches a heat source contact 404 and a heat sinkcontact 406 according to an embodiment of the invention and FIG. 4 b isa second perspective view of the thermoelectric generator 400 shown inFIG. 4 a . A first electrical contact 408 a, a second electrical contact408 b, a third electrical contact 408 c and a fourth electrical contact408 d are formed on a surface 410 of the heat sink contact 406 facingthe heat source contact 404. The thermoelectric fibers 402 are formedinto a serpentine shape that meanders back and forth between heat sourcecontact 404 and the heat sink contact 406. Specific portions of thethermoelectric fiber 402 in the foreground of FIGS. 4 a, 4 b will bedescribed it being understood that the remaining thermoelectric fibers402 shown in FIGS. 4 a, 4 b have corresponding portions. As indicated inFIG. 4 the foreground thermoelectric fiber 402 includes a first portion402 a that includes the cladding 204 and is in contact with the firstelectrical contact 408 a; a second portion 402 b that includes thecladding 204 and is in contact with the heat source contact 404, a thirdportion 402 c that does not include the cladding so that the core 202 isexposed also in contact with the first electrical contact 408 a, afourth portion 402 d including the cladding in contact with the heatsource contact 404, a fifth portion 402 e including the cladding incontact with the second electrical contact 408 b, a sixth portion 402 fincluding the cladding in contact with the heat source contact 404, aseventh portion 402 g with the core 202 exposed also in contact with thesecond electrical contact 408 b. As illustrated in FIGS. 4 a, 4 b theforegoing described cyclical pattern is repeated proceeding throughsuccessive contacts with the heat source contact 404 and the third andfourth electrical contacts 408 c, 408 d. Moreover, the length of thethermoelectric generator 400 may be extended relative the embodimentshown in FIG. 4 with the addition of additional electrodes. By thethermoelectric effect a potential difference is established betweensuccessive electrical contacts, e.g., between the first electricalcontact 408 and the second electrical contact 408 b; and between thesecond electrical contact 408 b and the third electrical contact 408 c.While each potential difference may be small, the potential differencesadd up in series to a larger total potential difference. An electricalload (not shown) may be connect between two electrical contacts, forexample between the first electrical contact 408 a and the fourthelectrical contact 408 d in order to draw power from the thermoelectricgenerator 400.

According to an alternative embodiment rather than using continuousfibers that span from the first portion 402 a to the seventh portion 402g, multiple separate segments are used. For example, the second portion402 b and the sixth portion 402 f may be deleted to break thethermoelectric fiber 402 into multiple segments.

FIG. 5 a is a front view of a spinneret 500 used to spin co-axial cladcore fibers along with a schematically illustrated high voltage source501 and a fiber collector 503 according to an embodiment of theinvention and FIG. 5 b is a cross-sectional view of the spinneret 500shown in FIG. 5 a . The spinneret 500 includes a top threaded fitting502 that leads into an inner conduit 504. The inner conduit 504 passesthrough an outer chamber 506. The inner conduit 504 extends from the topthreading fitting 502 to an output end 504 a located below the outerchamber 506. Disposed co-axially about the inner conduit 504 is an outerconduit 508 that extends from within the outer chamber 506 to an outputend 508 a located around the output end 504 a of the inner conduit 504.A side threaded fitting 510 leads into the outer chamber 506 and is influid communication with the outer conduit 508. A first electrospinningsolution (not shown) for forming a core of a co-axial clad corethermoelectric fiber may be introduced into the top threaded fitting 502and flow to the output end 504 a of the inner conduit 504. A secondelectrospinning solution (not shown) for forming a cladding of aco-axial clad core thermoelectric fiber may be introduced into the sidethreaded fitting 510 and flow into the outer conduit 508 within theouter chamber 506 and out of the output end 508 a of the outer conduit508. A high voltage established between the spinneret 500 and thecollector 503 by the high voltage source 501 causes the first and secondelectrospinning solutions to be accelerated into a reduced diameterstream which is then collected in the form of co-axial clad core fiberson the collector 503.

FIG. 6 a shows a broken out sectional front view of a spinneret 600 forspinning co-axial clad core fiber 200 and including an electromagneticvalve 602 for selectively interrupting a flow of cladding spinningsolution 601 and shown with the electromagnetic valve 602 in a closedstate according to an embodiment of the invention and FIG. 6 b is abroken out sectional view of the spinneret 600 shown in FIG. 6 a withthe electromagnetic valve 602 in an open state. The spinneret 600includes an outer chamber 604 which serves as a valve body. An innerconduit 606 passes through the outer chamber 604. The inner conduit 606includes an input coupling 606 a for introducing a core spinningsolution 603 and an outlet end 606 b for expelling the core spinningsolution 603 to form the core 202 of a co-axial clad core fiber 200being spun. Flow through the inner conduit 606 is not controlled by thevalve 602 but may be controlled by an external valve (not shown). Theouter chamber 604 includes an input coupling 605 for introducing thecladding spinning solution 601. The outer chamber 604 includes a lowerfunnel portion 607 terminated by an outer chamber outlet 609. An insideconical surface of the lower funnel portion 606 serves as a valve seat607 a. A compression spring 610, a pusher 612 and a plunger 614 aredisposed in the outer chamber 604. The compression spring 610 exerts adownward force on the pusher 612 which in turn exerts a downward forceon the plunger 614. Alternatively a different type of biasing elementmay be used in lieu of the compression spring 610. The plunger 614 has aconical lower surface 614 a which engages the conical valve seat 604 a.Thus, the compression spring 610 urges the conical lower surface 614 ainto engagement with the valve seat 604 a and stops a flow of thecladding spinning solution 601. The inner conduit 606 passes through acentral bore 614 b in the plunger 614. In inner groove 614 c is formedin the central bore 614 b of the plunger 614 and a sealing ring 616 isaccommodated partially in the inner groove 614 c and establishes a sealbetween the central bore 614 b and the inner conduit 606 to preventunwanted flow of cladding spinning solution 601 through the gap betweenthe inner conduit 606 and the central bore 614 b of the plunger 614.

A solenoid 618 is supported on an inner flange 620 a of a solenoidsupport 620. Leads 618 a pass from the solenoid 618 out of the outerchamber 604 to a control signal generator (not shown) for selectivelyactuating the solenoid 618. The plunger 614 suitably includes aferromagnetic material (e.g., as a powder dispersed in a polymericmatrix) or is made out of a ferromagnetic material (e.g., steel oriron). When the solenoid 618 is activated the plunger 614 is pulledupward allowing for passage of the cladding spinning solution 601between the conical lower surface 614 a and the conical valve seat 607a. The electromagnetic valve 602 can be selectively operated to cut offthe flow of cladding spinning solution 601 in order to spin the exposedportions of the core 206 shown in FIG. 2 according to certainembodiments of the invention.

According to alternative embodiments of the invention the end portionsof cladding material is etched away by dipping the ends of thethermoelectric fiber into an etchant. An etchant that preferentiallyetches the cladding material may be used to limit possible over etchinginto the core.

FIG. 7 shows a perspective view of a thermoelectric cloth 700 accordingto an embodiment of the invention. The thermoelectric cloth 700 includesa first set of threads 702 running in a first direction substantiallyperpendicular to the plane of the drawing sheet and a second set ofthreads 704 (a limited number of which are numbered to avoid crowdingthe drawing) woven through the first set of threads 702 runninggenerally perpendicular to the first set of threads 702. The first setof threads 702 includes a first pair of conductive threads 702 a and asecond set of conductive threads 702 b. The sets of conductive threads702 a, 702 b may, for example, include metal threads or conductivepolymer threads. The second set of threads 704 include co-axial cladcore thermoelectric threads 706. A first portion 706 a of thethermoelectric threads 706 includes the cladding 204 and is contact withthe first set of conductive threads 702 a. A second portion 706 b of thethermoelectric threads 704 which does not include the cladding 204, hasthe exposed core 202 which is in contact with the second set ofconductive threads 702 b. A third looped portion 706 c of thethermoelectric fibers 706 is located between the first portion 706 a andthe second portion 706 b juts out of the cloth 700 to facilitate contactwith a heat source (not shown). In operation when the thermoelectriccloth 700 is warmed, by action of the thermoelectric effect, anelectrical potential is generated between the cladding 204 which is incontact with the first pair of conductive threads 702 a and the core 202which is in contact with the second pair of conductive threads 702 b. Anexternal load (not shown) may be connected between the first pair ofconductive threads 702 a and the second pair of conductive threads 702 bin order to extract power from the thermoelectric cloth 700. Thethermoelectric cloth 700 may be used to construct a garment such as anundershirt, or winter coat, so that human body heat can be used as theheat source to drive thermoelectric power generation. Such power, mayfor example be used to power portable electronics such as for example anRF, visible or infrared emergency locator beacon (not shown).

FIG. 8 a is a perspective end view of a hollow thermoelectric fiber 800according to an embodiment of the invention; FIG. 8 b is a side view ofthe hollow thermoelectric fiber 800 shown in FIG. 8 a ; and FIG. 8 c isa cross-sectional side view of the thermoelectric fiber 800 shown inFIGS. 8 a, 8 b . The hollow thermoelectric fiber 800 includes an insideapproximately cylindrical surface 802 and an outside approximatelycylindrical surface 804. In certain embodiments the hollowthermoelectric 800 may be an electrospun nanoscale fiber having a wallthickness of 100 to 200 nanometers. Thermoelectric power generationefficiency is enhanced by increasing electric conductivity ofthermoelectric elements and decreasing thermal conductivity. Withinthermoelectric materials phonons conduct heat and increasing phononscattering leads to decreased thermal conductivity. In nanoscaledevices, phonon scattering at the surfaces is a significant contributionto phonon scattering. By making the thermoelectric fiber 800 hollow thesurface area available for phonon scattering is increased leading todecreased thermal conductivity and increased thermoelectric performance.The hollow thermoelectric fiber 800 may be p-doped or n-doped. Asdescribed below a thermoelectric device may include both p-doped andn-doped thermoelectric fibers. The thermoelectric fibers may be made ofa variety of materials such as mentioned above in the context of FIG. 2. In certain embodiments the hollow thermoelectric fibers may be made ofdoped silicon carbide that is electrospun from a doped silicon carbideprecursor. A method of making the hollow thermoelectric fiber 800 isdescribed below with reference to FIG. 14 .

FIG. 9 a is perspective view of a thermoelectric generator 900 includinghollow thermoelectric fibers 902, 904 of the type shown in FIGS. 8 a-8 cand FIG. 9 b is a partially exploded view of the thermoelectricgenerator 900 shown in FIG. 9 a . The thermoelectric generator 900 maybe used as a laboratory testbed for evaluating the performance ofthermoelectric fibers 902, 904 but may also be adapted for real worldapplications. The thermoelectric generator 900 includes a radiofrequency (RF) induction coil 906 winding around but not contacting anRF susceptor 908. An RF power source (not shown) is used to energize theRF induction coil 906. Referring particularly to FIG. 9 b , anelectrically insulating separator plate 910 is positioned adjacent tothe susceptor 908. A first set of thermoelectric fibers 902 of a firstdoping type (P or N) and a first electrical contact block 912 arepositioned one side of the separator plate 910, and a second set ofthermoelectric fibers 904 of a second doping type (opposite to that ofthe first set of thermoelectric fibers 902) and a second electricalcontact block 914 are positioned on an opposite side of the separatorplate 910. The first set of thermoelectric fibers 902 electricallycontacts the first contact block 912. The second set of thermoelectricfibers 904 electrically contacts the second electrical contact block914. The sets of thermoelectric fibers 902, 904 are positioned proximatethe RF susceptor 908 and are suitably electrically connected to eachother by a conductive metal film (not visible in the perspective ofFIGS. 9 a, 9 b ) formed on a surface of the RF susceptor 908 facing thethermoelectric fibers 902, 904. An insulating sleeve 916 fits around thethermoelectric fibers 902, 904; electrical contact blocks 912, 914 andthe separator plate 910. In a real world application a source of wasteheat such as an engine exhaust manifold may be substituted for the RFinduction coil 906 and susceptor 908. An electrical power load (notshown) may be connected to the first electrical contact block 912 andthe second electrical contact block 914 in order to draw power from thethermoelectric generator 900.

FIG. 10 is a side view of a doubly clad P-I-N co-axial fiber 1000according to an embodiment of the invention. The fiber 1000 includes asemiconducting outer cladding 1002 of a first doping type (N or P) andundoped or substantially lower level doped inner cladding 1004 and asemiconductor core 1006 of a second doping type (opposite to the dopingtype of the outer cladding 1002). The fiber 100 may be used inthermoelectric devices or electronic circuit applications. End portions1008 of the inner cladding 1004 are exposed and end portions 1010 of thecore 1006 are exposed.

FIG. 11 is a broken out sectional elevation view of a spinneret 1100 forspinning the doubly clad co-axial fiber 1000 shown in FIG. 11 . Thespinneret 1100 includes an inner conduit 1102 for supplying spinningsolution for forming the core 1006. The inner conduit 1102 includes aninner conduit input coupling fitting 1104 for receiving spinningsolution and an inner conduit outlet 1106 for expelling spinningsolution for forming the core 1006. An intermediate chamber 1108 isdisposed about the inner conduit 1102 such that inner conduit 1102passes through the intermediate chamber 1108. The intermediate chamber1108 includes an intermediate chamber side inlet coupling 1110 forintroducing a spinning solution for forming the inner cladding 1004 andan intermediate chamber annular outlet 1112 disposed about the innerconduit outlet 1110 such the inner conduit outlet 1106 is disposed inthe outlet 1112 of the intermediate chamber 1108. Spinning solution isexpelled from the intermediate chamber annular outlet 1112 for formingthe inner cladding 1004. The spinneret 1100 also includes an outerchamber 1114 disposed about the intermediated chamber 1108. The outerchamber 1114 includes an outer chamber side inlet 1116 for introducingspinning solution for forming the outer cladding 1002 and an annularouter chamber outlet 1118 for expelling spinning solution to form theouter cladding 1002. The annular intermediate chamber outlet 1112 isdisposed in the annular outer chamber outlet 1118.

FIG. 12 a is a first perspective view of a thermoelectric generator 1200that includes a direct PN junction 1202 between thermoelectric fibers1204, 1206 according to an embodiment of the invention, and FIG. 12 b isa partially exploded perspective view of the thermoelectric generatorshown in FIG. 12 a . The thermoelectric generator 1200 includes a set ofP-doped semiconductor fibers 1204 and a set of N-doped semiconductorfibers 1206. The semiconductor fibers 1204, 1206 may be made of thematerials discussed above in reference to FIG. 2 . In certainembodiments the semiconductor fibers 1204, 1206 may be made from dopedsilicon carbide made by pyrolizing doped silicon carbide precursors. TheP-doped semiconductor fibers 1204 have first ends 1208 connected to afirst electrical contact 1210 and the N-doped semiconductor fibers 1206have first ends 1212 connected to a second electrical contact 1214.Second ends 1216 of the P-doped semiconductor fibers 1204 and secondends 1218 of the N-doped semiconductor fibers 1206 contact each otherforming the direct PN junction 1202. The first electrical contact 1210and the second electrical contact 1214 are formed on an electricallyinsulating, thermally conductive heat sink 1220. Alternatively the heatsink 1220 may be electrically conductive and an electrical insulationlayer may be formed between the electrical contacts 1210, 1214 and theheat sink 1220. The second ends 1216, 1218 of the thermoelectric fibers1204, 1206 including the PN junction 1202 are inserted into a recess1222 of a heat source contact 1224. Inserting the second ends 1216, 1218of the thermoelectric fibers 1204, 1206 into the recess 1222 enhancesradiative thermal coupling between the PN junction 1202 and the heatsource contact 1224. An external load may be connected between the firstelectrical contact 1210 and the second electric contact 1214 to drawpower from the thermoelectric generator 1200. By providing the direct PNjunction 1202 one can avoid using metallization to form an indirectjunction between P and N thermoelectric materials as in the case ofprior art designs. One benefit of not using metals on the hot side of athermoelectric device is that metals could limit the maximumtemperature, hence limit the electrical output. The heat source contact1224 may be contacted with a source of waste heat such as an exhaustmanifold of an internal combustion engine. Alternatively the heat sourcecontact 1224 may be placed in the focus of a solar concentrator.

FIG. 13 is a flowchart of a method 1300 of making a PN co-axial cladcore thermoelectric fiber according to an embodiment of the invention.In block 1302 a batch of silicon carbide precursor is combined with afirst type of dopant. One type of precursor that may be used ispolycarbosilane made. Another type of silicon carbide precursor that maybe used is polysilane. Both are available from by Starfire® Systems, Incof Malta, N.Y. Polycarbosilanes are also available from Nippon Carbon,Co of Japan. Another polymeric silicon carbide precursor that may beused can be synthesized by according to the teachings of U.S. Pat. No.6,020,447. In brief '447 patent teaches a process that involvesreductive coupling of chlorosilane to form polysilane in the presence ofultrasonification. The polymeric ceramic precursor may be dissolved in asolvent to produce a solution of polymeric ceramic precursor. A solventsuch as toluene, tetrahydrofuran or mixtures thereof may be used. Adopant precursor may be added to the solvent. A suitable p-type dopantprecursor is a phosphorous (III) organometallic compound e.g.,diphenylphosphino ethylene. A suitable polymeric precursor for makingn-type doped silicon carbide nanofibers can be made by dissolving SiCprecursor in a suitable solvent in which is dissolved a small amount ofdopant in a form of nitrogen containing species such as primary,secondary, or tertiary organic amines (e.g., melamine, ganidine),inorganic amines, organometallic silazanes. Other dopants may also bemade of boron, aluminum, and carbon containing organometallic compounds.

In block 1304 a second batch of silicon carbide precursor is combinedwith a second type of dopant. One of the first and second types ofdopants may be an N type dopant and the other of the first and secondtypes of dopants may be a P type dopant. In other words the first andsecond batches of silicon carbide precursors may include opposite dopanttypes.

In block 1306 the first and second batches of silicon carbide precursorwith respective dopants are supplied to separate input ports of aco-axial spinneret. By way of nonlimitive example, the first and secondbatches of silicon carbide precursor may be input to top threadedfitting 502 and side threaded fitting 510 respectively of the spinneret500 shown in FIGS. 5 a, 51 b , or to the input coupling 606 a and inputcoupling 605 respectively of the spinneret 600 shown in FIGS. 6 a , 6 b.

In block 1308 the spinneret is used to spin co-axial clad core siliconcarbide precursor fiber. Spinning or electrospinning may be implementedin block 1308. Alternatively co-axial extruding may be performed in lieuspinning. The first batch of silicon carbide precursor may be used toform the core and the second batch of silicon carbide precursor may beused to form the cladding.

Optionally in the course of electrospinning the flow of claddingmaterial is terminated for one or more periods of time in order to forma portion of the precursor fiber in which the cladding is absent so thatthe core is exposed.

In block 1310 the co-axial clad core silicon carbide precursor fiber ispyrolized to obtain a co-axial clad core silicon carbide precursor witha core and cladding having opposite doping.

Optionally, after block 1310 end portions of the cladding are etchedaway so as to expose the core.

In block 1312 the co-axial clad core silicon carbide fiber is assembledinto a thermoelectric device. By way of nonlimitive example the co-axialclad core silicon carbide fiber may be assembled into devices such asshown in FIGS. 3 a, 3 b ; FIGS. 4 a, 4 b or FIG. 7 .

FIG. 14 is a flowchart of a method 1400 of making a hollowthermoelectric fiber according to an embodiment of the invention. Inblock 1402 a fugitive core spinning feed stock material is prepared. Thefugitive core spinning feed stock is a material that disintegrates whenexposed to pyrolizing conditions. The fugitive core spinning feed stockmay for example include polyacrylonitrile (PAN), polystyrene (PS),polyurethane, polymethylmethacrolate (PMMA).

In block 1404 cladding spinning feed stock including a silicon carbideprecursor and dopant is prepared. The silicon carbide precursor anddopant may include materials described above in reference to FIG. 13 .

In block 1406 the doped silicon carbide precursor cladding feed stock issuppled to an outer annular conduit of a spinneret. By way ofnonlimitive example, referring to FIGS. 5 a, 5 b the cladding feedstockmay be supplied through the side threaded fitting 510 and outer conduitto the output end 508 a which has an annular shape. According to afurther nonlimitive example, referring to FIGS. 6 a, 6 b the claddingfeed stock may be supplied through the input coupling 605 of the outerchamber 604 to the outer outlet 609 which is annular shaped.

In block 1408 the fugitive core spinning feed stock is supplied to aninner conduit of a spinneret. By way of nonlimitive example, thefugitive core spinning feed stock may be supplied to the inner conduit504 of the spinneret 500 or to the inner conduit 606 of the spinneret600.

In block 1410 the spinneret is used to spin fiber having a doped siliconcarbide precursor cladding and a fugitive core.

In block 1412 the fiber spun in block 1410 is heated to transform thedoped silicon carbide precursor cladding to doped silicon carbide and toeliminate (disintegrate) the fugitive core, thus producing a relativelyhigh surface area, hollow doped silicon carbide fiber. Such a hollowsilicon carbide fiber has the aforementioned advantages related to arelatively high thermal resistances attributable in part to phononscattering enhanced by the increased surface area associated with theinner substantially cylindrical surface.

FIG. 15 is a flowchart of a first method 1500 of forming a deviceincluding a P doped fiber and an N doped fiber joined to form a PNjunction according to an embodiment of the invention. In block 1502 afirst batch of silicon carbide precursor is combined with a first typeof dopant. The silicon carbide precursor and the dopant may include thematerials described above with reference to the method 1300.

In block 1504 the first batch of silicon carbide with the first type ofdopant is supplied to a spinneret. The spinneret used in blocks 1504,1512 need not be a co-axial spinneret such as shown in FIGS. 5 a, 5 b, 6a, 6 b , 11. Rather the spinneret may be a standard type used forspinning monolithic, homogeneous fibers. However, alternatively aco-axial spinneret may be used to spin fibers with a fugitive core inorder to realize a device that includes a direct PN junction betweenhollow fibers.

In block 1506 the spinneret is used to spin fiber of silicon carbideprecursor that includes the first type of dopant.

In block 1508 the fiber of silicon carbide precursor is used pryrolizedto form obtain a silicon carbide fiber that includes the first type ofdopant.

In block 1510 a second batch of silicon carbide precursor is combinedwith a second type of dopant. The first and second batches of siliconcarbide precursor suitably include opposite dopant types. One batch mayhave P type dopant and the other batch may have N type dopant.

In block 1512 the second batch of silicon carbide precursor with thesecond type dopant is supplied to a spinneret.

In block 1514 the spinneret is used to spin fiber of silicon carbideprecursor that includes the second type dopant.

In block 1516 the fiber of silicon carbide precursor that includes thesecond type dopant is contact with the pyrolized silicon carbide fiberthat includes the first type dopant.

In block 1518 the contacted fiber of silicon carbide precursor thatincludes the second type dopant and is in contact with the siliconcarbide fiber that includes the first type dopant is subjected to hightemperature in order to pyrolize the silicon carbide precursors andobtain silicon carbide fibers with the first and second types of dopantsin contact thereby forming a PN junction. Because the diffusibility ofdopant species within the silicon carbide is low, it is expected thatthe process of first pyrolizing one fiber, then contacting the pyrolizedfiber with the unpyrolized second fiber, then pyrolizing the secondfiber will lead to a sharper PN junction.

The fibers made by the method 1500 may then be incorporated into athermoelectric device such as device 1200 shown in FIGS. 12 a , 12 b.

FIG. 16 is a flowchart of a second method 1600 of forming a deviceincluding a P doped fiber and an N doped fiber joined to form a PNjunction according to an embodiment of the invention. In block 1602 afirst batch of silicon carbide precursor is combined with a first typeof dopant.

In block 1604 the first batch of silicon carbide with the first type ofdopant is supplied to a spinneret.

In block 1606 the spinneret is used to spin a fiber of silicon carbideprecursor including the first type of dopant.

In block 1608 a second batch of silicon carbide is combined with asecond dopant type. One of the first and second dopant types may be Pand the other N.

In block 1610 the second batch of silicon carbide with the second dopanttype is supplied to the spinneret.

In block 1612 the silicon carbide precursor that includes the secondtype dopant is used to spin fiber.

In block 1614 the fiber of silicon carbide precursor that includes thefirst type of dopant is contacted with the fiber of silicon carbideprecursor that includes the second type of dopant. The fibers may besolid however alternatively the fibers may be spun with a fugitive coreresulting in hollow fibers.

In block 1616 the contacted fibers of silicon carbide precursor aresubjected to high temperature to obtain silicon carbide fiber with thefirst type of dopant in contact with the silicon carbide fiber with thesecond type of dopant thereby forming a PN junction.

The contacted fibers forming the PN junction that are obtained in block1616 may then be used in a thermoelectric device such as device 1200shown in FIGS. 12 a, 12 b . Alternatively the contact fibers forming thePN junction that are obtained in block 1616 may be used in an electronicor electric power circuit, e.g., as a diode rectifier.

FIG. 17 is a first perspective view of a thermoelectric generator module1700 that includes direct PN junctions 1702 between semiconductor fibers1704, 1706 on a heat source contact 1708 side and FIG. 18 is a secondperspective view of the thermoelectric generator module 1700 shown inFIG. 18 showing the PN junctions 1702 between semiconductor fibers 1704,1706 inserted into black body cavity holes 1802 in the heat sourcecontact 1708. The semiconductors fibers 1704, 1706 include P-dopedsemiconductor fibers 1704 and N-doped semiconductor fibers 1706. In oneembodiment that is tat is particularly suitable for use with a hightemperature (e.g., above 1000 C) heat source the semiconductor fibersmay be doped silicon carbide fibers. Alternatively other materialsdiscussed hereinabove may be used. Each PN junction 1702 is a contactpoint between a pair of semiconductor fibers including one P dopedsemiconductor fiber 1704 and one N-doped semiconductor fiber 1706. AP-doped semiconductor fiber 1704 from one such pair and an N-dopedsemiconductor fiber 1706 from an adjacent pair are connected byelectrical traces 1710 that are formed on a heat sink contact 1712. Thesemiconductor fibers 1704, 1706 extend from the black body cavity holes1802 to electrical contact holes 1714 (a limited number of which arenumbered to avoid crowding the drawing) in the heat sink contact 1712.The semiconductor fibers 1704, 1706 may be brazed into the electricalcontact holes 1714 using a brazing material (not shown). Such brazingmaterial may form an electrical coupling between the semiconductorfibers 1704, 1706 and the electrical traces 1710. Multiple pairs ofsemiconductor fibers are connected in series by the electrical traces1710. A first set of through holes 1716 are provided in the heat sourcecontact 1708 and a second set of through holes 1718 are provided in theheat sink contact 1712. Terminals 1720 extend from the left most andright most (in the perspective of FIGS. 17-18 ) electrical traces 1710and may be used to connect the thermoelectric generator module 1700. Inoperation, by the agency of the thermoelectric effect, a temperaturedifference between the heat source contact 1708 and the heat sinkcontact 1712 will cause electrical power to be output through theterminals 1720. Thus, thermoelectric generator module 1700 may be usedas a standalone thermoelectric generator. Alternatively as shown inFIGS. 19-20 and discussed below the module 1710 may be connected toother modules of the same type.

An aerogel 1722 is provided in the space between the heat source contact1708 and the heat sink contact 1712. The P-doped semiconductor fibers1704 and the N-doped semiconductor fibers 1706 extend through theaerogel 1722. The aerogel 1722 may be deposited between the heat sourcecontact 1708 and the heat sink contact 1712 after assembly of the module1700. The aerogel 1722 serves to increase the thermal resistance betweenthe heat source contact 1708 and the heat sink contact 1710 which driveselectrical power generation. The aerogel 1722 also serves to protect theelectrical traces 1710 and any brazing from high temperatures of theheat source contact 1708.

The semiconductor fibers in any of the other thermoelectric generatorsdescribed herein may also be immersed in aerogel.

FIGS. 19-20 are perspective views of a thermoelectric generator 1900that includes four modules 1700A, 1700B, 1700C, 1700D of the type shownin FIGS. 17-18 . Bolts passed through the through holes 1716 in the heatsource contacts 1708 and holes 1718 of the heat sink contact 1712 areused to secure the four modules 1700A, 1700B, 1700C and 1700D together.Electrical bridges 1902 are used to connect the modules 1700A, 1700B,1700C, 1700D electrically. Two output terminals 1904 are provided toextract electrical power from the thermoelectric generator 1900.

FIGS. 21-22 are perspective views of a thermoelectric generator module2100 that includes direct PN junctions 2102, 2104 between semiconductorfibers 2106, 2108 at both a heat source contact 2110 and a heat sinkcontact 2112. The thermoelectric generator module 2100 includes P-dopedsemiconductor fibers 2106 and N-doped semiconductor fibers 2108 whichare connected in series. The semiconductor fibers 2106, 2108 alternatealong the series, such that except for at the ends of the series, eachP-doped semiconductor fiber 2106 is preceded and followed by one of theN-doped semiconductor fibers 2108. A first group of PN junctions 2102between the fibers are located at the heat source contact 2110 and asecond group of of PN junctions 2104 are located at the heat sinkcontact 2112. PN junctions from the first group 2102 and second group2104 alternate along the series of fibers 2106, 2108. The first group ofPN junctions 2102 are thermally coupled to the heat source contact 2110by being inserted into a series of holes 2114 in the heat source contact2110. The heat source contact 2110 may be operated at a sufficientlyhigh temperature (e.g., above 1000 C) such that radiative coupling iseffective in transferring heat from the heat source contact 2110 to thefirst set of PN junctions. The second group of PN junctions 2104 may bebrazed using a brazing material 2116 into a set of holes (filled withbrazing material 2116 and hence not visible) in the heat sink contact2112). Ends of the series fibers 2106, 2108 are connected to electricaloutput terminals 2118 located at the heat sink contact 2112. An aerogelmaterial 2120 is disposed between the heat source contact 2110 and theheat sink contact 2112. The series of fibers 2106, 2108 passes throughthe aerogel material 2120. The aerogel 2120 functions as discussed abovein reference to FIGS. 17-18 .

FIG. 23 is a cross-sectional view of a jet engine 2300 that includes asemiconductor fiber based thermoelectric generator 2302 according to anembodiment of the invention. Referring to FIG. 23 , the jet engine hasan outer housing 2304, which has an intake end 2306 at the left of thedrawing sheet and a thrust exhaust end 2308 at the right of the drawingsheet. An axial shaft 2310 is centered within the housing 2304. Theaxial shaft 2310 may include subcomponents not distinctly shown. Nearerto the intake end 2306 the axial shaft carries a set of compressor fans2312 and nearer to the thrust exhaust end (nozzle) 2308 the axial shaftcaries a set of turbine fans 2314. A combustion chamber 2316 defined byan inner circumferential combustion chamber wall 2318 and an outercircumferential combustion chamber wall 2320 is disposed about the axialshaft 2310 between the compressor fans 2312 and the turbine fans 2314. Afuel system (not shown) supplies a combustible fuel to the combustionchamber 2316. In operation, combustion in the combustion chamber drivesthe turbine fans 2314 which in-turn drive the compressor fans 2312. Thesemiconductor fiber based thermoelectric generator 2302 is located in anaxially extended circumferential space between the outer circumferentialcombustion chamber wall 2320 and the outer housing 2304 of the jetengine 2300. In operation combustion in the combustion chamber sets up athermal gradient between the outer circumferential combustion chamberwall 2320 and the outer housing 2304 of the jet engine. Thethermoelectric generator 2302 used in the jet engine 2300 may be of anyof the types described above and reference is made to the descriptionshereinabove for the particular details thereof. By way of nonlimitingexample in the case that the thermoelectric generator 2302 of the jetengine 2300 includes the thermoelectric generator module 2100 shown inFIGS. 21-22 the heat source contact 2110 will be thermally coupled tothe outer circumferential combustion chamber wall 2302 and the heat sinkcontact 2112 will be thermally coupled to the outer housing 2304.

FIG. 24 is an enlarged broken out portion of the jet engine 2300 shownin FIG. 23 including the nanofiber based thermoelectric generatorposition around a combustion chamber of the jet engine; and

FIG. 25 shows a partially sectioned portion of a rocket engine 2500including a double walled nozzle 2502 accommodating a semiconductorfiber based thermoelectric generator 2504 according to an embodiment ofthe invention. Referring to FIG. 25 , a lower portion 2506 of a rockettube 2508 is attached to the double walled nozzle 2502. The doublewalled nozzle 2502 includes an inner wall 2510 and an outer wall 2512.The semiconductor fiber based thermoelectric generator 2504 is disposedbetween the inner wall 2510 and the outer wall 2512. In operation heatedcombustion products exiting the rocket engine through the nozzle 2502(flowing within the inner wall 2510) and cooler ambient air streamingpast the outside of the nozzle (in contact with the outer wall 2512)will establish a thermal gradient between the inner wall 2510 and theouter wall 2512 through the thermoelectric generator 2504, therebydriving electrical power by the thermoelectric generator. Thus, inoperation the inner wall 2510 will have a temperature greater than theouter wall 2512. The thermoelectric generator 2504 is thermally coupledto the inner wall 2510 and the outer wall 2512. The thermoelectricgenerator 2504 may be of any of the types described above and referenceis made to the descriptions hereinabove for the particular detailsthereof.

The jet engine 2300 shown in FIGS. 23-24 and the rocket engine 2500 aretwo forms of thrust propulsion engines. Thrust propulsion enginesgenerally include a thrust exhaust (e.g., double walled nozzle 2502,thrust exhaust end [nozzle] 2308) that operates at high temperature, andaccording to a broader class of embodiments a thermoelectric generatoris integrated in the thrust exhaust of a thrust propulsion engine.Referring again to FIGS. 23-24 according to an alternative embodimentthe thrust exhaust end (nozzle) 2308 is made in a double wallconfiguration analogous to the double walled nozzle 2502 and athermoelectric generator is integrated between the inner and outer wall.

By way of nonlimiting example in the case that the thermoelectricgenerator 2502 of the rocket engine 2500 includes the thermoelectricgenerator module 2100 shown in FIGS. 21-22 the heat source contact 2110will be thermally coupled to the inner wall 2510 of the nozzle 2502 andthe heat sink contact 2112 will be thermally coupled to the outer wall2512 of the nozzle 2502.

FIG. 26 is a graph 2600 including plots 2602, 2604, 2606, for three testruns, of voltage versus temperature difference between hot and coldsides for a thermoelectric generator according to an embodiment of theinvention. The abscissa of the graph indicates the aforementionedtemperature difference in degrees Celsius or Kelvin and the ordinateindicates a corresponding thermoelectrically induced voltage inmillivolts. The thermoelectric generator for which the test results areshown in FIG. 26 includes solid silicon carbide fibers doped withphosphorous. The silicon carbide fibers were surroundedyttria-stabilized zirconia aerogel.

FIG. 27 is a graph 2700 including plots 2702, 2704, 2706, for three testruns, of Seebeck coefficient versus temperature difference between hotand cold sides for the same thermoelectric generator for which data isshown in FIG. 26 . Certain embodiments of the present invention exhibitSeebeck coefficients of at least 500 μV/K, more preferably at least 1000μV/K, and even more preferably at least 2000 μV/K.

FIG. 28 is a graph 2800 including plots 2802, 2804, 2806, for three testruns, of Seebeck coefficient versus temperature difference between hotand cold sides for another thermoelectric generator according to anotherembodiment of the invention. The thermoelectric data for which the datais shown in FIG. 28 included hollow boron doped SiC fibers. The fiberswere prepared by electrospinning a polycarbosilane SiC precursor, curingin a nitrogen atmosphere with about 60 ppm oxygen, followed bypyrolyzing by heating in an argon ambient from room temperature to 1000C at a temperature ramp rate of 1 degree C. per minute. Hafnia Oxideaerogel was formed in-situ around the SiC fibers thereby encapsulatingthe SiC nanofibers in Hafnia Oxide aerogel. The aerogel withencapsulated SiC fibers has then aged by heating in air to 500 C for 15minutes. One method of initially forming the aerogel that may beemployed in constructing thermoelectric generators disclosed herein isdisclosed by A. E. Gash et al “New sol-gel synthetic route to transitionand main group metal oxide aerogels using inorganic salt precursors”,Journal of Non-Crystalline solids 285 (2001) 22-28. Certain embodimentsof the present invention the aerogel includes an early transition metal.According to certain embodiments the aerogel includes an a group IVtransition metal. According to certain embodiments the aerogel includesan element selected from the group consisting of titanium, zirconium andhafnium.

FIG. 29 is a scanning electron micrograph of a hollow porous SiCsemiconductor fibers 2902 that may be used in a thermoelectric generatoraccording to certain embodiments of the invention. The fibers 2902include a generally cylindrical wall 2904 defining a generallylongitudinal hole 2906 generally centered within each fiber 2902. Thegenerally cylindrical wall includes and a multitude of pores 2908 in theSiC generally cylindrical wall 2904. The spinneret 500 shown in FIGS. 5a, 5 b and the method 1400 shown in FIG. 14 may be used to make thehollow porous SiC semiconductor fibers. In this case polyurethane wasused as a fugitive core material and without wishing to be bound to anyparticular theory regarding the porousity it is believed that the choiceof polyurethane led to the creation of the pores 2908 during the curingand/or pyrolyzing steps (discussed above in reference to FIG. 28 ).

FIG. 30 is a graph 3000 including plots 3002, 3004, 3006, 3008 for fourtest runs, of Seebeck coefficient versus average temperature of hot andcold sides for a thermoelectric generator including the hollow andporous SiC fibers shown in FIG. 29 .

In this document, relational terms such as first and second, top andbottom, and the like may be used solely to distinguish one entity oraction from another entity or action without necessarily requiring orimplying any actual such relationship or order between such entities oractions. The terms “comprises,” “comprising,” or any other variationthereof, are intended to cover a non-exclusive inclusion, such that aprocess, method, article, or apparatus that comprises a list of elementsdoes not include only those elements but may include other elements notexpressly listed or inherent to such process, method, article, orapparatus. An element proceeded by “comprises . . . a” does not, withoutmore constraints, preclude the existence of additional identicalelements in the process, method, article, or apparatus that comprisesthe element.

In the foregoing specification, specific embodiments of the presentinvention have been described. However, one of ordinary skill in the artappreciates that various modifications and changes can be made withoutdeparting from the scope of the present invention as set forth in theclaims below. Accordingly, the specification and figures are to beregarded in an illustrative rather than a restrictive sense, and allsuch modifications are intended to be included within the scope ofpresent invention. The benefits, advantages, solutions to problems, andany element(s) that may cause any benefit, advantage, or solution tooccur or become more pronounced are not to be construed as a critical,required, or essential features or elements of any or all the claims.The invention is defined solely by the appended claims including anyamendments made during the pendency of this application and allequivalents of those claims as issued.

We claim:
 1. A thrust propulsion engine including a first wall and asecond wall and a thermoelectric generator disposed between the firstwall and the second wall wherein the thermoelectric generator comprises:a heat source contact; a heat sink contact; and a plurality of co-axialfibers, each of said co-axial fibers comprising a core having a firstdoping type and a cladding having a second doping type disposed aboutsaid core, said plurality of co-axial fibers extending from said heatsource contact to said heat sink contact.
 2. The thrust propulsionengine according to claim 1 wherein said heat sink contact furthercomprises a first electrical contact and a second electrical contact,wherein said core extends beyond said cladding so as to present anexposed portion of said core, said cladding is electrically coupled tosaid first electrical contact and said core is electrically coupled tosaid second electrical contact.
 3. The thrust propulsion engineaccording to claim 1 wherein said heat source contact includes a holeand said plurality of co-axial fibers have ends inserted in said hole.4. The thrust propulsion engine according to claim 1 wherein saidplurality of co-axial fibers have a serpentine shape that meanders backand forth between said heat source contact and said heat sink contact.5. The thrust propulsion engine according to claim 4 wherein said heatsink contact further comprises a first electrical contact and a secondelectrical contact and wherein proceeding along a length of a particularco-axial fiber of said plurality co-axial fibers, said particularcoaxial fiber includes: a first portion at which said cladding iselectrically coupled to said first electrical contact; a second portionthermally coupled to said heat source contact; a third portion at whichsaid core is exposed and is electrically coupled to said secondelectrical contact.
 6. The thrust propulsion engine according to claim 1wherein said first wall is a nozzle inner wall and said second wall is anozzle outer wall.
 7. The thrust propulsion engine according to claim 1wherein the first wall comprises a wall of a combustion chamber and thesecond wall comprises a housing wall, and the thrust propulsion enginecomprises a jet engine.
 8. The thrust propulsion engine according toclaim 1 comprising a rocket engine.